Three-phase power circuit breakers conventionally have an electrical contact structure which includes three movable contact arms, one for each pole unit, which are connected to an electrical load, and associated relatively stationary contacts connected to a three-phase AC power source. A drive bar links all three movable contact arms for simultaneous opening and closing movement thereof, with the drive bar and contact arms being hereinafter called "movable contact means". A stored energy operating mechanism rapidly moves the movable contact means to a closed position in which electrical contacts on the contact arms engage the relatively stationary contacts.
Energy is stored in springs during the closing movement, with the springs aiding in rapid disengagement of the contacts when the circuit breaker is manually tripped, and when it is automatically tripped due to a circuit problem, such as over current and under voltage. When a circuit breaker is tripped, it is important that the movable contact means be rapidly accelerated to an open position in order to initiate rapid and effective arc interruption. The movable contact means has substantial inertia, and thus it is also important that the movable contact means be stopped at the desired open position without rebound, which could cause re-striking of an arc, and without damage to the movable contact means or other circuit breaker components.